Vintage Dirt Bike Q & A

is the oil injection on a 75' MT250 typically reliable? I know you can blind it off on a boat motor and mix your gas. Anyone done this?

Mine is blocked off because I have a reed valve on it and wasnt going to drill a hole in it for the oil feed. It works fine like this but you have to have oil and a mix cup when you go to the gas station.

Cool. So all I need is a set of reeds and a plate? There is a place also for oil. I assume that is separate.

No sorry the reed valve setup I have was custom made by rich at richs tailored porting. You can still just block off your oil pump and put a bolt in the manifold and it will be fine. I used a piece of alluminum bar to make the block off plate and a piece of cork gasket to go under it, it works fine no problems.

You can easily block it off and use pre-mix. I've done this on a bike that I had to modernize the carb and it didn't have a port for oil injection as used on the original. I could have easily drilled out a port and installed a nipple but decided to just pre-mix. This was on a 1979 yamaha dt100.

I've also just cleaned out an original oil pump from a 37 year old biked and it works just fine. (1974 Kawasaki 350 f9 bighorn) However, I'm a little leery of the oil pumps in these old bikes. It's too easy to premix to gamble. I would like to hear other opinions also. I haven't ridden the f9 often enough to in any way gauge the reliability. But I haven't seen any real objections to it in all the years I have been enjoying 2 stroke bikes.

When I worked on the f9, I used a 50:1 premix in the fuel tank and monitored the oil pump flow through the clear tubing that I used. I could see the oil was moving because of a few air bubbles in the line were shifting. I also had checked the oil injector port because it is easily accessible with the rotary induction system. I removed the carb and turned the flywheel with a drill and socket to engage the oil pump and it was shooting oil as it should. For a carb mounted injection, just remove the oil supply tubing and do the same as I did. You should see oil coming from the tubing.

To use or not to use, that is the question....

nola_fiddy
1979 cr125r - no frills pre-mix guzzler!

I prefer to use pre-mix at 32:1 in my MT/CR250. The previous owner had disconnected the pump. He also had to bore the engine next size over & replace the piston, etc. This leads me to believe that the mixer either failed or the wrong oil was used.

Now if you plan to commute or ride the bike long distances it would be nice to pull up to the fuel pump & just fill it up. Just depends upon your plans. Pre-mix done correctly will never let you down.

~JM~

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